Field of the Invention
The present invention relates to a calibration apparatus and a control method thereof.
Description of the Related Art
Calibration is a known technique that makes the display characteristics of a display apparatus closer to the desired characteristics. In calibration, an evaluation image (patch image) is displayed on a display apparatus, and the optical characteristics (e.g. brightness and colors on the screen) of the evaluation image are measured by a photometer. Then the image quality of the evaluation image is adjusted so that the measured optical characteristics become closer to the desired characteristics. For example, the image quality is adjusted by adjusting the values of parameters which are used for image processing. By repeating display, measurement and image quality adjustment of the evaluation image, the display characteristics of the display apparatus can be brought closer (or maintained at) the desired characteristics.
Prior art on calibration is disclosed, for example, in Japanese Patent Application Laid-open No. 2005-249596. Japanese Patent Application Laid-open No. 2005-249596 discloses a technique of performing calibration using a non-contact photometer, while considering the influence of external light (ambient light: light other than light from the display surface).
In order to perform appropriate (correct) calibration using an external photometer (photometer installed outside the display apparatus), the photometer must be correctly installed. In concrete terms, a correct measurement result (measurement result of light from the display surface) may not be acquired if the distance between the photometer and the display surface (screen) of the display apparatus is too far, or if the light receiving direction of the photometer is diagonal with respect to the display surface. Specifically, the light from the display surface may not reach the light receiving unit of the photometer, or external light may enter the light receiving unit, which makes it impossible to acquire a correct measurement result. If an incorrect measurement result is acquired, an incorrect calibration result is acquired. As a result, the display characteristics diverge from the desired characteristics because of this incorrect calibration. And if the user edits the image using the display apparatus of which display characteristics have diverged from the desired characteristics, the edited image may be different from the desired image. For example, the edited image may have colors that are different from the desired colors.
As a prior art that solves this problem, a technique to detect an installation failure of the photometer is known. For example, an expected range, which is a range of expected measurement values (range of measurement by the photometer), is set, and if a measured value outside the expected range (inappropriate value: abnormal value) is acquired, it is determined that an installation failure occurred to the photometer. If an installation failure occurs to the photometer, calibration is force-ended, whereby an incorrect calibration result reflected on the display characteristics can be prevented.
However if a narrow expected range is set to accurately detect an installation failure, a measurement value becomes a value outside the expected range only because of a slight change in the measurement value. This means that an installation failure can be accurately detected in a dark room environment, which is not influenced by external light very much, on the other hand, in an environment which is easily influenced by external light, an installation failure is frequently detected, and calibration is often force-ended.